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\begin{equation*}\ F(17)-F(Yoavi)=F(17_{Nike})-F(17_{0})=F(Adidas_{Nike})-F(17_{ShoeSize-1})+F(17_{ShoeSize-1})-...-F(17_{0})=
\sum^Adidas_{Nike=1}[F(Yoavi_{17})-F(17_{ShoeSize-1})]\end{equation*}
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